Men At Arms takes place not long after the events in Guards! Guards!. (I recommend reading that one first; there are some details there that will influence the plot in this book.) Captain Vimes is on his way out the door to an early retirement; his impending marriage to Lady Sybil will make him a gentleman of leisure. The City Watch, part of the Patrician's diversity program, has hired on three new cadets, just as inept as the current Night Watch, so they fit in quite well, although one's a dwarf, one's a troll and one's a woman. Actually Angua, the woman, was hired to fit the diversity quota of being a supernatural (she's a werewolf), but the guards don't realize this until much later. Carrot still is the best watchman Ahnk-Morpork has ever seen.

An assassin, Edward d'Eath, gets a silly notion that the city would work better if the monarchy could be restored. This will interlock with the back story for Carrot already revealed in Guards! Guards!. D'Eath steals an artifact from the assassins guild (I'll give you a hint, the cover artist really liked it and it's had to assassinate someone with a wolf head.) This artifact seems to have a mind of its own, though, and, like all Discworld novels, hijinks ensue.

Much like Lords and Ladies, this Discworld novel is darker than the previous ones. Pratchett is beginning to use Discworld to reveal the darker sides of human nature (and heroic sides as well). A somewhat major character even dies, and not in a I-saw-this-coming-all-along kind of way.